International Publication WO/91/07078 discloses an aerator which injects high pressure liquid intermittently through a nozzle into the turf to form holes for aerating the turf, and a pressing roller which smooths the injected turf while the aerator travels on the turf.
According to the aerator described in the International Publication WO/91/07078, one pressing roller is provided in the front of and another one at the back of a nozzle system including a plurality of nozzles arranged in the lateral direction of the aerator, respectively, the frontward and backward pressing rollers rock integrally with the nozzle system as viewed from the side of the aerator such that the nozzle system and the pressing rollers are maintained at an appropriate level despite an irregularity on the ground in the travelling direction.
The problems of the aerator in the International Publication WO/91/07078 are as follows.
(a) Although the nozzle system and the pressing rollers follow the irregularity of the turf in the travelling direction of the aerator, they can not follow the irregularity of the turf in the lateral direction of the aerator. Thus the level of the aerator becomes inappropriate if there is such an irregularity in the lateral direction of the aerator.
(b) As mentioned above, one pressing roller is disposed in front of and one at the back of the nozzle system, respectively, and the turf can be easily damaged due to the weight of these rollers. Further, since the degree of smoothing of the ground by the pressing rollers depends on their weight, such weight is preferably increased, thus causing still more damage to the turf.
The conventional aerator for turf also does not possess a special safety function as regards the injection of high pressure liquid through the nozzle.
Since the injection of high pressure liquid through the nozzle involves various dangers, safety measures for preventing erroneous operations by the operator must be adopted. From the safety point of view, the following matters should be taken into consideration.
(c) A nozzle system is lowered to be close enough to the ground to inject high pressure liquid into the ground to a predetermined depth at the injecting operation site, and when the aerator for turf travels on an ordinary road between the storage site and the injecting operation site, the nozzle system is raised to be kept appropriately apart from the ground. In this position where the nozzle system is raised, the injection of high pressure liquid through the nozzle should be prevented.
(d) The aerator for turf travels at a low speed during the injecting operation and at a high speed while travelling on an ordinary road, etc. Except during the injection operation, when the vehicle is travelling, injection of high pressure liquid through the nozzle should be prevented.
(e) In order to avoid an unloaded operation of the pump, the pump should be stopped when the liquid tank becomes empty.
In addition, in a golf course, the aerator for turf injects high pressure liquid such as liquid insecticides into the turf while travelling on the turf at regular intervals or as the occasion may demand. Since such an aerator for turf is equipped with various kinds of oil associated devices, oil may drop onto the turf and damage the turf or soil, if an accident to these oil associated devices of the aerator for turf should occur. In particular, since the appearance and beauty of the green of a golf course is strictly maintained, it is especially important that damage caused by oil leaking from the aerator for turf be prevented.
The conventional aerator for turf does not provide measures for preventing oil from leaking from the oil associated devices with which it is equipped.